Better Bombs: Scientists Develop Metal That Explodes on Impact

When most bombs go off, they release a spray of deadly shards of steel. Now, imagine that those shards were themselves explosive, detonating in a massive chain reaction. It's for real: Defense contractors are harnessing the strange alchemy of reactive materials (RMs) -- in which two or more inert materials are mixed to create an explosion -- to develop smaller, more lethal warheads, as well as new ways to protect troops against mortar rounds and rocket-propelled grenades.

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RMs generally consist of powdered metals, such as aluminum or titanium, combined with an oxidizing agent. Whether that agent is another powdered metal or a nonmetallic compound, such as Teflon, contact alone isn't enough to trigger an explosion. A powerful impact, however, will chemically mix the materials, igniting them and leading to a massive shock wave. "A big challenge is making [RMs] strong enough to survive launch, but fragile enough to react on impact," says Judah Goldwasser, program manager at the Office of Naval Research, which is developing RMs for potential use in antimissile systems. Instead of punching small holes in a target, Goldwasser says, RM shrapnel could cause an entire enemy missile to break up in midair.

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At press time, Pennsylvania-based DE Technologies said it was weeks away from demonstrating a defensive warhead that can detonate near an incoming grenade, mortar round or missile, spraying it with explosive RM shrapnel. Part of the Army's Active Protection System program, the warhead will detonate threats at a safe distance, while possibly limiting the risk of friendly fire. (Unlike steel shrapnel, RM shards can be made to burn out quickly.)

Not surprisingly, RMs are also being developed for offensive purposes. The Air Force is working on a warhead called BattleAxe that will shower a large area with reactive fragments, devastating "soft" targets such as trucks. Cluster bombs often leave behind dangerous unexploded munitions, but stray RM fragments are safe to handle, which would help lower civilian casualties following military operations. Accidental drops won't set RM fragments off, and they can be tossed in a fire to burn up.

Despite their potential, it could take years for RMs to reach the battlefield. There's no deployment date for the Army's defensive system, and BattleAxe development will run through 2009, with possible deployment years later.

This Navy test of a prototype warhead showed that reactive materials -- inert compounds that ignite on impact -- can increase the radius and lethality of a missile.